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cygonaut
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Posted: Mon Sep 21st, 2009 09:15 am |
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NASA has begun serious studies about privately-owned "space taxis," a good idea. Commercializing human transportation into low Earth orbit and back down to Earth would free NASA to optimize its next spaceship — the Orion — for deep space missions. That's a good plan. To get to the space station and other destinations near Earth, NASA can buy tickets on stripped-down taxis that will be a lot cheaper.
Ever since Apollo, NASA’s “people-mover” operation has relied on vehicles with capacities far in excess of what's needed to send spacefliers into Earth orbit and back. Some of the taxi design suggestions are astonishingly — even unbelievably — lightweight compared with what was used for Apollo orbital missions, let alone shuttle missions. I look forward to seeing better ideas along these lines.
What really intrigues me is that the moon is the perfect place to test out a revolutionary space transportation system — the "skyhook" or space elevator system. The concept has been around for a century: Essentially, just lower a rope from space to the ground, and use that to pull your payload into orbit.
Making the concept a reality in Earth orbit would be far beyond any credible near-term human capability. Not so at the moon. Its lower gravity and lack of atmosphere provide the perfect setting (and the perfect rationale) for a skyhook system that slowly spins as it orbits the moon, dipping its end near or onto the surface every two hours. The tether would have to be heavy, but it is well within the range of plausible space technology.
A "practical" concept for a lunar space elevator was described in Omni magazine by Bob Forward and Hans Moravec in 1981. Moravec expanded upon the idea in 1986, saying the skyhook system would offer "a fine alternative to rockets for getting supplies and personnel to and from the lunar surface."
Such a system could be tested on a small scale at first, and then ramped up incrementally. That's the beauty of this Flexible Path approach: Each step in capabilities leads to the next step within reasonable reach. Giant leaps into the unknown are not called for. Decades-long projects aren't needed. Each new goal is well within the office term of the president who endorses it.
Targeting asteroids
Orion spacecraft (perhaps, as proposed for safety, in pairs) can venture farther from Earth, eventually paying visits to passing asteroids. Accessible asteroid orbits tend to have very long synodic ("repeat opportunity") periods, so there's no time to launch a robotic probe and operate it for a few years before a crew arrives.
It would make sense to dispatch a smaller probe that gets to the asteroid a few weeks before the humans do, to map it and later relay communications to surface operations both human and robotic.
Missions to asteroids could address three fundamental human motivations: curiosity, greed and fear. Scientifically, they are of tremendous value as records of the solar system's history. Materially, they may contain resources (water more valuable than metals) that could be economically exploited for space activities. And in practical terms, knowing how rigid asteroids are may be a matter of life and death someday, when one of them has to be nudged off a dangerous Earth-approaching path.
On to Mars?
The next step could be to send astronauts and robotic supply ships toward Mars, perhaps using high-efficiency ion engines or plasma engines related to the Chang Drive. The initial voyages would have the astronauts stop short of an actual Martian landing. However, there should be no frustration involved here — the mission will be challenging and rewarding enough.
Mars has two very convenient "asteroids" right next door, its moons Phobos and Deimos. They would provide radiation and thermal shielding, material support (perhaps water) and a base of operations for human scientists to run robots in real time on the Martian surface. Beyond Earth, these locations may be the safest place for long-term stays anywhere else in the inner solar system.
Here, the presence of humans near Mars shows its value. With no radio signal travel time, remote operators could drive the rovers and run the sampling equipment in essentially real time. They could control fleets of small and large robots on the surface.
The two Mars rovers currently in operation, Spirit and Opportunity, are mighty impressive. But even the rover team's chief scientist, Steven Squyres, has said that all their science and sampling and snooping around over the past five years at Mars could have been accomplished by a human field geologist in a week. Humans on Mars could move and decide a hundred times faster. But humans near Mars, combined with robots on Mars, offers the best of both worlds: safe access for the robots, plus fast human control from a few thousand miles away.
Surface samples could be rocketed up from the robot fleet on small, simple boosters and retrieved by scout ships sent out from bases on the Martian moons. Eventually, people could descend to the Martian surface. That part is easy since Mars allows air braking. Surface-to-orbit taxis, perhaps modeled after the stripped-down high-efficiency vehicles developed commercially here on Earth over the next few years, would follow. And at some point, with experience from operating at the moon, a Mars-based rotating skyhook system could supplement, or entirely replace, rocket transportation up from the surface.
Imaginary missions ... for now
These are all still imaginary missions. But here's the bottom line: by not getting trapped into replaying old strategies with admittedly better (but operationally unchanged) hardware, new paths made possible by more capable technologies and more informed imaginations could be much more attractive.
The "look but don't touch" option could become "reach out and grab" sooner than any other option — even the options that call for a lot more spending. If such a choice is seriously being considered, we should be careful to treat it with respect and hope, and not instinctively take the side of the moonies and the Marsies and the other destination-driven partisans who have been stepping up to the microphones lately.
It makes so much sense it's almost scary. It's so rational that its political prospects must be slim. So let's not strangle it in the crib.
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Above consists of excerpts from:
http://www.msnbc.msn.com/id/32767421/ns/technology_and_science-space/
NBC News space analyst James Oberg spent 22 years at NASA's Johnson Space Center as a Mission Control operator and an orbital designer.
Last edited on Mon Sep 21st, 2009 09:17 am by cygonaut
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